List the two main propositions of Oparin and Haldane.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: Oparin and Haldane were scientists who proposed a theory regarding the origin of life on Earth. Their ideas contributed significantly to the field of evolutionary biology.

2. **First Proposition**: The first main proposition by Oparin and Haldane states that life could have arisen from pre-existing non-living organic molecules. This suggests that the building blocks of life were formed from simpler organic compounds that were not alive.

3. **Second Proposition**: The second main proposition is that the formation of life was preceded by chemical evolution. This means that before life could emerge, there was a process of chemical evolution where diverse organic molecules were formed from inorganic constituents.

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